Signaling apparatus and method



July 26, 1932. 1.. 1.. NETTLETON SIGNALING APPARATUS AND METHOD Filed Dec. 8, 1927 2 Sheets-Sheet m u mm k N im mm PMN w R NW N RN %w i wm MN ww 9? mm. Wm mm a s w W MNN w\ a w Q MW INVENTOR: L .A. Matt/atom,

aha-W July 26, 1932.

L. L. NETTLETON SIGNALING APPARATUS AND METHOD Filed Dec. 8, 192 2 Sheets-Sheet 2 llii i.

mm M QM mu INVENTOR. 41.1... Watt Zeta n 1?, Q'K-V Patented July 26, 1932 UNITED STATES MON 01* PENNSYLVANIA PATENT orncl:

LEwIs L. NETTLETON, or EDGEWOOD BOROUGH, PENNSYLV NIA, AssIeNon To THE UNION SWITCH & SIGNAL ooMPANY, or swIssVA n, PENNSYLVANIA, A ooR Pon- SIGNALING APPARATUS AND METHOD Application filed. December 8, 1927. Serial No. 238,567.

My invention relates to signaling apparatus and particularly'to apparatus for and methods of signaling between two points on a railway train, such for example, as between the locomotive and the caboose of a freight train; or between the locomotive at the front, and a second locomotive at the rear, of the train. More particularly my present invention relates to signaling systems inwhich the signals are transmitted through the me dium of the usual train brake pipes contain ing fluid under pressure.

I will describe several forms of signaling apparatus and several methods embodying 1 my invention, and will then point out the novel features thereof in claims. In the accompanying drawings, Figs. 1 ant 2, when placed end to end with Fig. 1 on the "r prises a receiver R and a transmitter T left, form a diagrammatic View illustrating one form of apparatus employed in a method of signaling embodying my invention. Fig. 3 is a diagrammatic View showing a modified form of a portion of the apparatus shown in Figs. 1 and 2, and also embodying my invention.

brake pipe which is normally supplied with fluid pressure (usually compressed air) and which controls the brake applying apparatus in the ordinary and well known manner. The apparatus shown in Fig. 1 is assumed to :.-I be located at the head-end of the train and comprises a transmitter T and a receiver R The apparatus shown. in Fig. 21s assumed to be located at some other polnt on the train, such for example, as the caboose, and com- I will first describe the apparatus involved in the transmission of signals from the transmitter T to the receiver R The brake pipe A is normally supplied with fluid pressure from a suitable source of-pressu're not shown 1n the drawings, through pipe 1, a relay valve D, pipe 2 and the usual feed valve 46 and enginemans brake valve 47. The relay valve D comprises a slide 5 operated by a piston f 6, which is normally held in its lower-posiphere through port 9 of valve E. Whenwinding 8' of valve E is energized, however, the port 9 1s blanked and fluid prcssure'flows from a source not shown in the drawmgs through pipe? and valve'E to the underside I of piston 6. It will be noted that the area of piston 6 upon which the fluid pressure so supplied is effective'is greater than the area of the piston subjected to the pressure from pipe 1, so that the piston 6 moves upwardly, carrying with"jit slide 5,into 'a'position in which the slide blanks pipe 2 and connects the brake pipe A with atmosphere through pipe 3 and a restricted'orifice 4. As a result, the pressure in thebrake pipe is reduced.- If, now, the valve E is again de-energized, the piston 6 returns to its lower position, blank-- ing pipe 3, and recharging the'brake pipe through valves46 and 47. It follows there fore that each time valve E is operated, a

pressure impulse is impressed uponthe air in the brake pipe A which impulse is caused by withdrawing a quantity of'air from the brake pipe to momentarily reduce the pres sure, and immediately thereafter admitting" air to the brake pipe to restore the-pressure to which the pipe is normally charged.

Int-he present embodiment of my invention, the valve E is controlled automatically by certain apparatus now to be described and which is also at timesused in connection with thereception of signals from other points alongth-e brake pipe. I

The reference character F designates 'a magnet valve comprising a winding 14- arranged when energized to open the valve, under which conditions fluid pressure is supplied to a reservoir 17 from a suitable source not shown in the drawings throughpipe 13,

valve F and pipe 16. Reservoir 17 iscon' nected with a pressure limiting valve Q through pipes 16 and 20. Valve Q comprises a plate 18 urged against the pipe 20 by a spring 19. It follows that when valve F is open, reservoir 17 is charged to a predeter- 5 mined ressure which depends upon the force exert by the spring 19 against the plate 18. If this pressure is exceeded, the valve Q opens to reduce the pressure in reservoir 17. It will be plain, therefore, that during the'time interval that valve F is operated, the reservoir 17 becomes charged to a predetermined pressure. Reservoir 17 is also connected with atmosphere through one or the other of two restricted orifices 29 or 30. When the manually operable valve H occupics the position in which it is'illustrated the drawings, reservoir 17 is connected with 7 atmosphere through orifice 29;

Two pneumatic relays G and K are responsive to the pressure existing in reservoir 17 .Each of these pneumatic relays comprises avdiaphragm 2.1 subjected to the pressure in the-'reservoir-and controllinga plunger 23 wbichis biased to one position by a spring 22..v When the reservoir 17is charged, plungers 2310f pneumatic relays G and K are moved tothe right'sothat relay G closes frontcontact 25 and relavK closes front contact27. If valve 13 is closed; after the contacts 24aand26. At theexpiration of a furthertiine interval, the relay-K will oper ate to open front contacti27 and close back contact 28. Itwill be plain that the times required for-operation of relays G and K after the-closing of valve F depend upon the rate 1 of pressure reduction in; reservoir 1.7. When valve H occupies the position shown in the -drawings,.the time required foroperation-of the relays G and K will be different from the-time required by these relays-when valve H is reversed to connect pipe 16 wit-h atmosphere through orifice 30.

Two slowreleasing relays M and P and V certain apparatusassociated therewith, ,op-

eratein connection with the reception of signals from other points along the brake.

pipe as. well as for the control of transmitter T the change-over being accomplished by a manually operable switch X having a lefthand or receiving position vand ;a righthand or transmitting position. In explaining the operation of the transmitter T I will first-assume that the switch X is closed in its transmitting position so that contacts 10 10 11-11. and 1-2'12 are closed. The closing of contact 1111 completes a circuit forrelay M which may be traced from terminal Bofa suitable-source of energy not shown reservoir -17 has been charged to the press in the drawings, through back contact 28 of pneumatic relay K wire 31, contact 1111 of switch X, wire 32, and winding of relay M to terminal C of the same source. Relay 1V1 therefore becomes energized. ingof front contact 33 of relay lVP completes a circuit for relay P from terminal B, through front contact 33 of relay M wires 34, 35 and 36, and winding of relay P to terminal C. During the brief interval after the energization of relay M and before relay P picks, up duerto current supplied over the pick-up circuit just traced, a circuit is closed for. winding 14 of magnet valve F from terminal B, over front contact 33 of relay M wires 34 and 37, back contact 38 of relay P wire 39, and winding 14 of magnet valve'F to terminal C. During the in terval required for relay 1 to open its back contact therefore, magnet valve F is energized, thereby supplying fluid pressure to reservoir 17, and charging this reservoir to the pressure determined by valve Q Pressure thus supplied to reservoir 17 operates relays G and K to close their front contacts and open their back contacts. The opening of back contact 28 of relay K interrupts the circuit for relay M which thereupon becomes de-energized, breaking the pick-up circuit already traced for relay P at front Contact 33 of relay M Relay P is maintained in its energized condition, however, by current which flows from terminal B, over front contact 25 of relay G wires 40 and 36, and winding of relay P to terminal C.

As soon as valve F became closed, pressure in reservoir 17 commences to blow down through the orifice 29. After the expiration of a time interval, relay G returns to its original position, thereby opening front contactr25 to de-energize relay P and closing back contacts 21 and 26. W hcn back contact 26 closes, current flows from terminal B,

throughxback contact 26 of relay (3- wire k 113, contact 1O1O of switch X, wire 114E,

and winding 8 of valve E to terminal C. Valve E is therefore operated to supply fluid pressure to the underside of piston 6 of valve AS a result, valve D operates to disconnect the brake pipe A from pipe 1 and to connect the brake pipe with atmosphere through pipe 3 and restricted orifice 41. The operation of relay G also completes a circuit from terminal B, through a signaling device, q, here shown as a bell 12, wire 43, contact 12-12 of switch X, wire 44, back contact 24 of relay G wire 45, front contact 27 of relay K to terminal C. At the expiration of a brief interval of time following the operation 1 of relay G the pressure in reservoir 17 will be sufiiciently reduced to permit the operation of relay K lVhen this happens contact 28 closes'so that relay M is again energized to commence the cycle of operation just described. The opening of front contact 27 of 7 The clos- 5 P A through two passages 49 and.v 50.

G interrupts the circuit for magnet valve E,

thereby allowing valve D to return to its original position so that the pressure in brake pipe 8, orifice 4 and the brake pipe A is restored to its original value. It follows therefore that as long as switch X is closed in its transmitting position, the cycle of operations,

just described, is continued, and valve E is operated intermittently to impress pressure impulse variations upon the area of the brake pipe A. By properly proportioning the Various parts, the length of each pressure impulse and the time interval between successive impulses can be adjusted to any desired value. I have discovered. satisfactory results can be obtained by making the interval during which the brake pipe is connected with atmosphere one second long and by making the interval between successive impulses of valve E approximately 10 seconds duration. Thus when valve E is closed in its transmitting position, pressure impulses of approximately one second duration are impressed upon the air in the brake pipe at a frequency of one impulse in 10 seconds;

The pressure impulses impressed upon the air in the brake pipe may be used to control receiving apparatus located in the brake pipe in any suitable manner. One form of apparatus for operating in accordance with these pressure impulses is illustrated in R This apparatus comprises a reservoir 51 which is connected with a branch pipe 48 communicating with a brake pipe A check valve 52 is interposed in the passage 49 to permit .air to flow the reservoir 51 but to prevent the flow of air through this passage in the opposite direction. In similar manner a check valve 53 is interposed in passage to permit the flow of air from the reservoir 51 to the brake pipe through passage 50, but to prevent the flow of air through this passage in the opposite direction. The reference character 54 designates a member of material having a high temperature resistance co-eflicient such as platinum and which member in the form here shown comprises a fine wire supported by an insulating block 55 and exposed to air flowing through the passage 50. In similar manner a second platinum wire 56, supported by a block 57 is suspended in passage 49. The wires 54 and 56 are connected in series with two windings and 59, respectively,

' relay J from the brake pipe into' of. a diiierential relay J 2 which is supplied with energy from a battery 58. The current from the battery 58 normally heats the wires 54 and 56 to a comparatively high temperature and the parts are so proportioned that under normal conditions, that is, when the air in brake pipe A is not subjected .to periodic pressureimpulses, the effect of the current in winding 60 of relay J upon the arma-' ture 62 predominates over the efiect of current in winding 59 upon this armature. When the air in the brake pipe A is subjected to a pressure variation, air flows into or out of reservoir 51 through one of the passages 49 or 50. I will assume that the transmitter T is being operated to periodically reduce the pressure in the brake pipe and then restore the pressure to its original value. Each time the pressure in the brake pipe A is reduced, air tends to flow from the reservoir 51 into the brake pipe A because the reservoir 51 is normally charged to the same pressure as the brake pipe. The difference in pressure between the reservoir 51 and the brake pipe A causes a flow of air through valve 53 and passage 50 past the heated wire 54, but no air can flow from reservoir 51 to the brake pipe A through passage 49 because valve 52 is closed. The flow of air past the heated wire 54 0001s this wire and decreases its resistance but the temperature of wire 56 is not changed because there'is no flow of air past this wire. The decrease in the resistance of wire 54'causes a correspond ing increase in the current in winding 59 of Under these conditions the effect of winding 59 upon armature 62 predominates so that the relay is reversed and contact 6161 is closed. When the pressure in the brake pipe is next restored to its original value the pressure in the brake pipe will be greater than that existing in reservoir 51, so that air will tend to flow from the brake pipe to the reservoir. The flow of air in this direction through passage 50 is prevented by check valve 53, but the air can flow in this direction through passage 49. As a result, the wire 56 is cooled but the wire 54 is allowed to return to its normal temperature because there is no flow of air past wire 54. It follows that the resistance of wire 56 is decreased and the resistance of wire 54 is increased. When this happens thearmature 62 of relay J 2 is restored to its original con dition, and contact 6161' opens.

It will be plain when the transmitter T isbeing operated,

the relay J is operated to close contact 61-61"? for a brief interval of approximately one second, once in each 10 seconds.

The relay J controls time measuring apparatus similar to that associated with transmitter T and comprising two slow releasing relays M and P which control a magnet valve F which in turn'controls two pneufrom the foregoing that relay J 2 opens, but relay P matic relays G and K Each time the relay J is operated .to close contact 61 61 current flows from terminal B, through contact 61 6l, wires 68 and 69, and the winding of relay hi to terminal C. Relay M therefore becomes energized and closes front contact 33. hen this contact is closed a pick-up circuit is completed for relay P from terminal B, over front contact 33 of relay M wires 34, 35 and 36, and winding of relay P to terminal C. Relay P therefore closes but during the brief interval after 'enrgiza tion of relay M and before the opening of back contact 38 of relay P a circuit is closed from terminal B, over front contact 33 of relay M wires 34 and 37, back contact 38 of relay P wire 39, and winding 14 of magnet valve F to terminal C. Magnet valve F 2 is therefore opened to charge reservoir 17 to a pressure which depends upon the adjustment of the pressure limiting .valve Q and pneumatic relays G and K operate to close their front contacts. ,Relay M becomes tie-energized as soon as contact 61-61 of is now held in its energized condition over'a stick circuit including contact 25 of relay G Reservoir 17 is constantly connected with atmosphere through a restricted orific 30 so that as soon as the valve F closes after relay P picks up, pressure in reservoir 17 commences to decrease. At the expiration ofa time interval relay G returns to its (n'iginal-position, thereby closing back contact 24. At the expiration of another brief interval, relay K will also return to its original position and open front contact 27. The parts are so proportioned however, that during the interval following the restoration of relay G and prior to the opening of front contact 27 of relay K relay J is again operated to close its contact 61-61, and current then flows from terminal B, through contact 61-61 of relay J wires 68 and 70, back contact 71 of relay M wire 72, back contact 24: of relay G wire 45, front contact 27 of relay K through a suitable signal, here shown as a bell N to terminal C. At the same time, of course, the operation of relay J again operates relay M andsets into operation the cycle already described. It should be pointed outhowever, that in order to operate the signal N the operations of relay J must occur at a predetermined frequency so that these operations occur during the brief interval that back contact 24 of'relay G is closed and front contact 27 of relay K? is also closed. 7 1

Of course any variation in the brake'pipe pressure,such for example, as occurs when a pressure reduction is 'made to cause an automatic application of the brakes, will result in a single operation of the relay J This operation of relayJ might successively operate relays M P, G and K but unless a second operation of relay J 2 occurs at exactly the proper time, relay M will not become operated. On the other hand, when the transmitter T is being operated, the signal N 2 will be operated each time a pressure impulse is impressed upon the air in the brake pipe. It follows, therefore, that with transmitting and receiving apparatus con structed in accordance With my present invention, signals may be transmitted through the compressed air in the brake pipe with substantially no interference due to impulses impressed upon this air by causes other than the transmitter.

F or sending signals from the rear end of the train to the head-end, I have discovered that the transmitter illustrated at the lefthand side of Fig. 2, and designated in general, by the reference character T gives excellent results. This transmitter comprises a reservoir 81 which is connected with atmosphere through pipe 83 when valve 82 is open, and which is connected with the brake pipe A through an orifice 79, and pipe 78, when valve 80 is open. A second reservoir 76 is connected with the brake pipe A through pipe 78 when valve 77 is open. A third reservoir 73 is constantly supplied with fluid at a pressure which is considerably higher than that existing in the brake pipe, from a source not shown in the drawings through pipe'7e. I This reservoir 73 is connected with reservoir 76 when valve 75 is open. As shown in the drawings, all of the valves 82, 80, 77 and 75 are closed. If a pressure impulse is to-be imposed upon the fluid in the brake pipe, valve 75 is first opened to charge reservoir 76 to the comparatively high pressure existing in reservoir 73. Valve 75 is then closed, to trap this higher pressure in reservoir 76. Valve 77 is next opened to discharge the measured volume of fluid with which reservoir 7 6 is now charged, into the brake piper-L, thereby impressing a sudden pressure increase on the air in the brake pipe. Valve 77 is then closed and valve 80 is opened thereby connecting reservoir 81 which previously contained.atmospheric pressure, with the brake pipe through restricted orifice 79. A volume of air therefore flows from the brake pipe into reservoir 81, and the parts are preferably proportioned in such manner that the volume of air required to charge reservoir 81 to normal brake pipe pressure is equal to the volume of air admitted to the brake pip-e when reservoir 76 is connected therewith. With-this proportioning of the parts the pressure in. the brake pipe is restored to its initial value when the pressure in reservoir 81 and the brake pipe are equalized. Valve 80 is then closed and valve 82 is opened to discharge reservoir '81 to atmos phere. \Vhen valve 82 is again closed, the parts are restored to their original condition and the cycle of operation of the valves may be repeated to impress successive pressure impulses upon the air in the brake pipe.

Although I have illustrated valves 82, 8O 77 and 75 as separate manually operable valves, it is apparent that they may be operated in any suitable manner, the only requirement being that'they shall operate in the prescribed order to first Charge and then discharge-the brake pipe to imposeperiodic pressure variations upon the air in the brake pipe. Even if the valves shown in Fig. 2 all operate manually,-they may be controlled in such manner that pressure variations are imposed upon the air in the brake pipe at the proper frequency to operate areceiving apparatus selectively responsive to the frequency of the variations imposed upon the brake pipe air. i

The receiver R shown in Fig. 1 is similar to the receiver R in operation, but differs in the precise arrangement of the parts. The receiver R comprises a reservoir 93 connected with the brake pipeA through pipe 84 and two passages 85 and 86 connected in parallel. Passage 85 is provided with a valve comprisinga perforated grid 87 covered with a disk 88 ofsome flexible material such as mica, which disk is held in place by a convex cover plate 89. WVith this arrangement it will be seen that aircan flow from the reservoir 93 throughthe perforations in the grid 87 to the brakepipe A, but that air tending to flow in the opposite direction will carry the mica disk 88 against the grid 87 and will prevent the flowof air in such direction. In similar manner a second perforated grid 90 is provided with a mica disk 91 held in place by a plate 92 to prevent the passage of air from the reservoir to the'brakep-ipe through passage 86, while allowing the flow of air through this passage in the opposite direction. The platinum'wire 54 carried by the insulated block is interposed in the path of air flowing from the reservoir 93 through passage 85-when this wire is connected in series with winding of a differentialrelay' J and battery 63. In similar manner the platinum wire 56, which is sub jected to the flow of air from the brake pipe to the reservoir 93through passage 86, is connected in series with winding 59 of relay J and battery 1 63. Under normal condi tions, that is, when the pressure in the brake pipe has a steady value, the reservoir '93 is charged to the same pressure as the brake pipe and the effect of winding 60 upon armature 62 of relay J predominatesover the effect of winding 59 uponthis armature, so that contact 61-61 is open. WVhen'an impulse is impressed uponthe air in the brake pipe, by transmitter T for example, the first increase of pressure. causes acurrent of air past wire 56, thereby decreasing the temperature of this wire and increasing the current in winding 59 of relayJ Therelay therefore closes contact 61 61. When the pressure in the brake pipe returns to its normal value, the air which flows from the reservoir 93 through passages 85 back into the brake pipe'decreas'es the temperature of wire 54, thereby increasing the current through winding 60 of the relay J but since there is no flow of air'past wire56, this wire returns to its original temperature and relay J again swings armature 62 to its normal position and opens'contact 6161 The relay J controls a signal. bell N through the same time measuring means which is used to control the transmitter T When this apparatus is used to co-operate with the relay J to receive signals impressed upon the air in the brake pipe, the changeover switch Xis moved to its receiving or lefthand position wherein contacts 11-11* and 1212 are closed. Furthermore, the valve His operated to connect the reservoir 17 with atmosphere. through restricted orifice 30 which is so proportioned as to give a different time for the blow-down of the reservoir 17, which time is dfl'erent for operating the signal receiving apparatus than isaccom-. plished by the orifice 29 in connection with the control of the transmitter T With the switch X in its receiving position, each time contact 61-61 is closed, relayM becomes energized, current flowing from terminal B, through contact 6161"- of relay J wire 94, contact 11 11 of switch X, wire 32, and winding of relay M to terminal C. When relay M becomes energized it picks up relay P and energizes magnet valve F as explained hereinbefore. Reservoir 17 is thus charged to the pressure determined by valve P is also open, and the relay drops. When relay G returns to its normal position, a partial circuit is completed for'the, signaling device N andif, at this instant relay J again becomes operated, current flows from terminal B, through contact 61*, wire 95, back contact 71 of relay M wire 96, signaling device N wire 97, contact 1212 of switch X, wire 44, backcontact 24 of relay G wire 45, front contact 27 of relay K to terminalC. If, therefore, the frequency of operation of relay {J is such'that this relay closes its contacts during the interval after the closing. of back contact 24 of relay G and prior to the opening of front contact 27 of relay K an impulse of energy will be delivered tothe signaling device N to operate this device. If, however,-the time interval between successive impulses, of rela-y J is greater or less than the time interval elapsing between the pick-up relay M and the returnof relayK- to its normal position, the signaling device N will not be operated.

A modified form of receiving apparatus which is responsive to variations in the brake pipe pressure is illustrated in Fig. 3. Refer ring to this view, the reservoir 98 is connected with brake pipe A through a pipe 99 containing a restricted-passage 100'. A U- .tube having a restriction 101 is filled with a liquid 106 such as oiland has its ends ter minating in two chambers 102 and 103 respectively. The chamber 102 contains a flexible diaphragm 104 which is subjected to the pressurein the brake pipe. The chamber 103 contains a diaphragm 105'subjected to the pressure in reservoir 98. Under normal conditions, that-is when the pressure in the brake pipe is not being varied, the pressure in the brake pipe and the reservoir 98 will be equalized-through the pipe 99 and the passage 100. Under these conditions, the pressures in chambers 102 and 103 will be equal and the contact 107 controlled by diaphragm 105 will be open. If, however, a pressure impulse is im pressed upon the air in brake pipe A so that the pressureof this air suddenly increases, the pressure in chamber 102 will be greater than the pressure in chamber 103, so that the liquid 106 in the U-tube S will flow through the restriction 101, thereby lifting diaphragm 105 to close contact 107. At the same time, this temporary increase in brake pipe pressure is conducted through passage 100 to increase the pressure in reservoir 98. After the pressure in the brake pipe has been restored the pressure in the reservoir 98 will be higher than that existing in the brake pipe and the diaphragm'105 will be depressed, forcing the liquid 106 through the restriction 101' and opening contact 107. In similar manner if the first part of the pressure impulse impressed upon the air in the brake pipe is a decrease in pressure, the diaphragm 105 will be depressed by the comparatively large pressure then existing in reservoir 98. But some of this pressure will cause air to flow from reservoir 98 through the passage 100 into the brake pipe A. When the brake pipe pressure is restored, therefore, to its normal value, it will exceed the pressure in reservoir 98 and the diaphragm 105 will then be raised, closing contact 107.

To permit rapid equalization of large pressure changes in the brake pipe, pipe 108 connects the brake pipe andreservoir through a check valve 109 which permits air to flow from the reservoir into the brake pipe if the pressure difference exceeds apredetermined amount.v In similar manner if the pressure in the brake pipe exceeds the pressure in-the reservoir 98 by a predetermined amount,

check valve 111 will open to permit the equalization of air through pipe 110.

be used to control time measuring means such as illustrated in Figs. 1 and 2 in the same manner as contacts 616l of the relays J and J It Will therefore be seen that with apparatus embodying my invention, pressure impulses are impressed upon the fluid of the brake pipe at a predetermined frequency and that each of these impulses sets into operation means which measure the time between successive impulses and permit the operation of the signaling means only if the interval between successive impulses has a proper duration.

Although I have herein shown and described only a few forms of signaling apparatus and a few methods of signaling embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combinationwith a pipe containing a fluid subjected to periodic pressure variations, a reservoir connected with the pipe through two parallel passages, two check valves one in eachpassage for permitting the flow of said fluid through such passages in opposite directions, two wires one in each saidpassage and each having a high temperature-resistance co-efiicient, a relay havmg two windings, and a circuit for each winding including one of said wires.

2. In combination, a pipe containing a fluid under pressure, means for impressing periodicpressure impulses of a predetermlned frequency upon the fluid in said pipe,

a main relay responsive to such pressure impulses, a reservoir connected with atmosphere through a restricted orifice, means controlled by said relay for at times admitting fluid to the reservoir to charge the reservoir to a predetermined pressure, two pneumatic relays connected with said reservoir and arranged to be operated when the reservoir is charged but to return to their normal conditions successively as the pressure in thereservoir is dissipated through said orifice, a signal, and

means for operating said signal when said main relay is in operated condition provided one pneumatic relay is in normal condition and the other pneumatic relay is in operated condition.

3. Incombination with a train brake pipe containing fluid under pressure, means for lmpresslng periodic pressure impulses of predetermined frequency upon such fluid, a mamrelay arranged to close its contact in response to each such pressure. impulse, a

first slow-releasing relay, a circuit for said first slow-releasing relay including said contact of the main relay, a second slow-releasing relay, a pick-up circuit for said second slow-releasing relay including afront contact of the first slow-releasing relay, a reservoir separately connected with atmosphere through a: restricted orifice and a pressure limiting valve, a magnet valve arranged when energized to connect the reservoir with a source of fluid pressure, a circuit for the magnet valve including a front contact of the first slow-releasing relay and a back contact of the second slow-releasing relay, a first and a second pneumatic relay both connected with said reservoir and both arranged to close their front contacts when the reservoir is charged but to successively close their back contacts in the order mentioned as the go pressure in the reservoir decreases, a stick circuit for the second slow-releasing relay including a back contact of the first pneumatic relay, a signal; and a circuit for said signal including the contact of the main relay, a back contact of the first slow-releasing relay, a back contact of the first pneumatic relay, and a front contact of the second pneumatic rela L In combination with a pipe normally 80 charged with fluid pressure, a first magnet valve, means effective when said first valve is operated to impress a pressure impulse upon the fluid in said pipe, a reservoir separately connected with atmosphere through a restricted orifice and a pressure limiting valve, a second magnet valve arranged when energized to connect the reservoir with a source of fluid pressure, a first and a second pneumatic relay arranged to close their 49 front contacts when the reservoir is charged and to successively close their back contacts in the order mentioned as the pressure in the reservoir decreases, a first slow-releasing relay, a circuit for said first slow-releasing relay including a back contact of the second pneumatic relay, a second slow-releasing relay, a circuit for said second slow-releasing relay including a front contact of said first pneumatic relay, a circuit for said first mag- 50 net valve including a back contact of said first pneumatic relay, a circuit for said second magnet valve including a front contact of said first slow-releasing relay and a back contact of said second slow-releasing relay, an electric signal, and a circuit for said signal including a back contact of said first pneumatic relay and a front contact of said second pneumatic relay.

In testimony whereof I affix my signature.

o0 LEWIS L. NETTLETON. 

